Rock drill



July 29,, W41. I J. c. CURTIS 2,251,224

ROCK DRILL Filed July ll, 1940 2 Sheets-Sheet l /5 g I I I /6 zm g 06323022 66 34 zflaim 6 [wre k 2 flwfimmt Y M J. c. CURTIS 1,

aocx DRILL Filed July 11, 1940 2 Sheets-Sheet 2 a? E 4 v Ex 62 g 905 .2 3-

& P -5 Patented July 29, 1941 UNITE ROCK DRILL John 0. Curtis, Claremont, N. H., assignor to Sullivan Machinery Company, a corporation of Massachusetts Application July 11, 1940, Serial No. 344,954

15 Claims.

This invention relates to rock drills, and more particularly to hole cleansing means for rock drills of the pneumatically operated hammer piston type.

In the drilling of rock, the use of water to keep down the dust hazard is generally necessary. The quantity of water that must be used varies more or less directly with the quantity of air which attains access to the hole being drilled during the drilling operation. Best results in drilling are generally accomplished when a relatively small quantity of water can be employed, for the water stream is seldom strong enough to carry out the larger particles of rock during the drilling of down holes, and the intermittent blowing operations which are necessary to clear the hole will be most effective when the smaller particles of rock, which the water stream is usually capable of carrying out of the hole, are not removed, but instead left so as to form a thicker and more muddy mixture of stone particles in the bottom of the hole, and thereby prevent the air from blowing through the larger particles so readily when the hole is blown. Moreover, when less water can be used, and air entrance with the water can be minimized, better working conditions from the standpoint of comfort are secured. These factors will be observed to establish the desirability of preventing, to the maximum possible extent, the access of air to the drill hole during normal drilling operations because less water will then be necessary. It will be evident, however, that while it will be desirable to adopt some expedient for avoiding the entrance of air to the hole during normal drilling, yet that expedient should be a simple one and should be such as not to impair the flow of the maximum quantity of air to the hole when a blowing operation is to be performed. Moreover, coordinated control of the water supply and of hole blowing and of the means provided to reduce the access of air to the hole during normal drilling, is very desirable.

It is an object of my invention to provide an the drill, and being operative to close the vent and supply compressed air to the drill steel chuck when the supply of cleansing liquid and the operation of the drill motor have been discontinued. Still another object is to provide in a rock drill of the above character an improved valve control means for controlling the supply of cleansing fluid to the drill hole. Still another object is to provide improved means for controlling the supply of pressure fluid to and the venting of pressure fluid from the drill steel chuck of a pressure fluid actuated drill. Yet a further object is to provide an improved coordinated control for hole blowing and cleansing liquid supply. These and other objects of the invention will hereinafter more fully appear.

In the illustrative embodim'ent of the invention there has been shown a preferred form and two modifications which the invention may assume in practice.

In the drawings:

Fig. 1 is a longitudinal sectional view through a rock drill having incorporated therein the preferred form of the invention and showing the throttle valve in drill-running position.

Fig. 2 is a longitudinal sectional view similar to Fig. 1 but showing the throttle valve in hole blowing position.

Fig. 3 is a detail sectional view through the throttle valve on a different plane from Figs. 1 and 2', also showing this valve in full open or on position.

Fig. 4 is a longitudinal sectional view through a portion of a rock drill having a modified form of vent control valve associated therewith.

Fig. 5 is a view similar to Fig. 4 but showing the vent control Valve in a different position.

Fig. 6 is a longitudinal sectional view similar to Figs. 1 and 2 but on a smaller scale, showing a further modified form of construction.

Fig. '7 is a fragmentary sectional view taken on the plane of Fig. 6 but showing the parts in a different position.

In the illustrative embodiment of the invention shown in Figs. 1 to 3 inclusive, the preferred form of the improved hole cleansing means is embodied in a rock drill, generally designated I, of the pressure fluid actuated, hammer type. The rock drill proper is of a current commercial design and comprises a cylinder 2 having a bore 3 containing a reciprocatory hammer piston 4. The hammer piston has a forwardly projecting striking bar 5, which is guided in a bushing B mounted within the forward portion of the cylinder 2 and the piston is adapted to deliver impact blows to the shank of a drill steel l. Formed in the striking bar are splineways 9 interengaging with splines on a chuck driver element lEl with which a steel rotating and supporting member II is appropriately interlocked, as at 12; the member I I being enclosed in a suitable chuck housing M secured to the forward end of the cylinder 2 in any well known manner. A pressure fluid actuated distributing valve mechanism I is mounted in a valve box It arranged at the rear end of the motor cylinder, and this distributing valve mechanism is adapted to control the supply of pressure fluid through suitable passage means to the motor cylinder to effect reciprocation of the hammer piston in a manner which will be understood by' those skilled in the art. The details of this valve mechanism and of the passages leading to the motor cylinder which are controlled by said valve mechanism need not be described, but it may be noted that the construction may be such as is shown in my copending application Serial No. 315,786, filed January 26, 1940, patented Dec. 17, 1940, No, 2,224,861. Conventional means is provided for rotating the drill steel as it is percussively actuated by the hammer piston, comprising a ratchet and pawl mechanism IS having a spirally grooved rifle bar slidingly interlocked with the hammer piston. As the hammer piston moves forwardly, the pawls of the ratchet and pawl mechanism permit the rifle bar to rotate so that the hammer piston delivers an unimpeded blow to the shank of the drill steel, and upon the return movement of the hammer piston the rifle bar is held against rotation by the pawls,.

and, due to the spiral groove connection between the rifie bar and piston, the piston is caused to rotate. The rotary motion of the piston is transmitted to the drill steel through the splineways 9, the chuck driver element It] and the steel sup-,

porting member I l. A throttle valve 2| arranged in a bore 22 in a rear cylinder head 23 is provided with a port 25 for conducting pressure fluid from a central supply passage 26 in the valve to a passage 2! opening into a pressure chamber 29.

will be noted that secured, as by a gland plug 32, within the back head 23 of the motor cylinder is a liquid conducting tube 33. The liquid conducting tube extends axially through alined bores in the hammer piston and rifle bar, and at its forward end opens into an axial bore 3 3 formed in the drill steel 7. The tube has a reduced portion at its forward end to provide a substantial clearance between the tube and the walls of the drill steel bore. Attached to the drill cylinder in any suitable manner is a valve mechanism, generally designated 36, for controlling the supply of cleansing and dust-allaying liquid from a supply line 31 to a passage 33 formed in the back head 23 and opening into a passage 39 in the gland plug, and the passage 39 communicates with the tube 33. The valve mechanism 36 comprises a housing t'having a bore 42 in which a bushing 43 is received and held in place by a plug 55 threaded into the end of the bore. A valve member 45 having a valve stem 41 extending through the bushing controls the flow of liquid from the supply line 31 through passages 48 in the bushing to a passage 50 in the housing fill leading to the passage 38 in the cylinder head. A spring 5| continuously urges the valve 6 towards its closed position and holds the valve stem against a plunger 52 reciprocably mounted in a bore 53 in the housing tit. When the throttle valve is in the position shown in Fig. 3, pressure fluid is supplied through an opening 55 in the valve and a passage 55 in the rear cylinder head, to the bore 53, where it acts on the plunger 52 and moves the valve 35 to its open position. Accordingly. when the throttle valve is in full running po sition, liquid will be supplied to the bottom of the hole being drilled.

Formed in the rearward portion of the drill steel supporting member H and in the forward portion of the chuck nut ii; is a chamber 58 within which the rear end of the drill steel shank projects to receive the impact blows of the piston striking bar. In this construction the chuck nut ID is provided with passages 59 opening into the chamber 58 and into a chamber 50 formed between the walls of the bushing 6 and the walls of the chuck housing M. The chamber 58 is connected through a passage 62 extending longitudinally through the cylinder 2, to a passage 53 in the rear cylinder head which opens into the bore 22 containing the throttle valve 2 l. Formed on the outer peripheral surface of the throttle valve is a groove 54 which connects the passage 83 with a vent port 65 in the cylinder head when the throttle valve is in a position to supply pressure fluid through the port 25 to the passage 2], pressure chamber 29 and the distributing valve mechanism 5 for effecting operation of the drill motor. A port 66 is provided in the throttle valve for supplying pressure fluid from the supplypassage 26 to the passage 63 when the valve is in the position shown in Fig. 2. With the throttle valve in this position, the ports 25 and 55 in the valve assume positions in which the supply of pressure fluid to the motor cylinder and to the passage 56 leading to the plunger 52 for opening the valve 56 is cut off. The passage 56 is connected instead through a groove 63 on the outer periphery of the throttle valve to a vent port 69 in the rear cylinder head, and with the pressure fluid vented from the plunger 52 the valve 45 is moved to its closed position by the spring 5|, thereby cutting (iii the supply of cleansing liquid to the drill hole. ressurefluid flowing from the supply passage 25 through the port 65 to the passage 53 enters thepassage 52 and is conducted to the chamber 69, from which it is supplied through the passages 55 to the chamber 58 at the rearward end of the drill steel. The pressure fluid in the chamber 58 acts on the end of the striking bar 5 to move the hammer piston towards the distributing valve mechanism l5, and the fluid flows around the reduced end of the liquid tube into the bore 34- in thedrill steel, whence it is conducted to the bottom of the drill hole for blowing out the cuttings. If the hammer piston is moved rearwardly a suificient distance to uncover at its forward end the cylinder exhaust port 3%, pressure fluid will flow from the chamber 56 through the splineways 9 in the striking bar to the cylinder boree and through the exhaust port 33 to atmosphere. In order to prevent the hammer piston from moving rearwardly and uncovering the exhaust port 30 during the hole blowingprocess and soreducing the effectiveness of the latter, there is provided a passage [6 connecting the rearward end of the cylinder bore 3 to the bore 22 for the throttle valve; and when the throttle valve is in the position of Fig. 2 for hole blowing, a port ll in the throttle valve connects the supply passage 26 to the passage ill.

The operation of this illustrative embodiment of the invention may be summarized as follows: With the throttle valve in the position shown in Figs. 1 and 3, pressure fluid will be supplied through the port 25, passage 21 and chamber 29 to the distributing valve mechanism l5, where it will be distributed through suitable passages to the cylinder bore for effecting reciprocation of the hammer piston. At the same time, pressure fluid will be supplied through port 55 and passage 55 to the plunger 52, moving the latter to force the valve 46 to its open position. Liquid is then supplied under pressure from the line 3'! past the valve 45, through passages 48, 53, 38 and 39, to the tube 33, where it is conducted to the bore 34 in the drill steel and led to the drill hole for washing away the cuttings from the bottom of the hole. The chamber 58 at the rear end of the drill steel is vented through passages 59, chamber 50, passages 52 and 63, groove 54 and vent port 55, to atmosphere, thus preventing pressure fluid escaping from the cylinder bore through the splineways in the striking bar from building up a pressure in the chamber 58 and passing through the bore 34 in the drill steel to the bottom of the drill hole. When it is desired to blow out the drill hole, the throttle valve is rotated to the position shown in Fig. 2. The ports 25 and 55 are then in positions cutting oif the supply of pressure fluid to the distributing valve mechanism I and to the valve control plunger 52. The groove 58 in the throttle valve connects the passage 55 to the vent port 69, and pressure fluid is vented from the plunger 52 so that the spring 51 moves the valve 36 to its closed position, cutting oh the flow of cleansing liquid to the drill hole. The port 65 in the throttle valve connects the pressure fluid supply passage 25 to the passage 53, and pressure fluid flows through passage 52, chamber 55 and passages 59 to the chamber 58. Pressure fluid in the chamber 58 acts on the end of the hammer bar, forcing the hammer piston partially towards its rear cylinder head, and also flows through the bore 34 in the drill steel to the bottom of the drill hole for blowing out the latter. The port "H in the throttle valve connects the supply passage 26 to the passage for supplying pressure fluid to the rear end of the cylinder bore, where it acts on the hammer piston and prevents the latter from moving rearwardly to a position where pressure fluid could be vented from the chamber 55 through the splineways 9, cylinder bore 3 and exhaust port 36, to atmosphere.

In the modification shown in Figs. 4 and 5, the construction is much the same as that described, except that a valve 73 reciprocably mounted in a bore M in the chuck housing It controls the communication of passages 59 with the passage 52 or with a very direct vent port '55 formed in a cap 16 which is threaded into the lower end of the bore M. A spring 18 continuously urges the valve 13 in a direction to connect the passages 55 to atmosphere. When the throttle valve is in a position to supply pressure fluid to the passage 52, the valve 73 is forced by the pressure fluid against the action of spring 18 to a position connecting the passage 62 through passages 59 to the chamber 58. When, however, the throttle valve is in the position corresponding to that of Figs. 1 and 3, the chuck is vented to atmosphere without having to be connected therewith through the throttle valve groove 54 and the port 55.

In the modification of the invention shown in Figs. 6 and 7, a throttle valve arranged in a bore 8| in a rear cylinder head 52 is provided with a port 83 for connecting a pressure fluid supply passage 84 to a passage 85 leading to a pressure chamber 81. The chamber 8'! is connected through a passage 88 to a valve chamber 89, from which a distributing valve distributes the pressure fluid through suitable ports and passages St and 55 to the cylinder bore for effecting reciprocation of the hammer piston 4. Blows are transmitted to the drill steel 1 by the striking bar 5, and the splineways 9 in the striking bar interlock with the splines in a chuck nut 9|, which in this case is threaded into a chuck sleeve 2 and transmits the rotary motion of the hammer piston to the drill steel. An exhaust port 93 substantially centrally located between the ends of the cylinder bore is provided for exhausting pressure n'uid from the cylinder bore to atmosphere. A passage 5 formed in the cylinder opens to atmosphere at a point adjacent the exhaust port 53 and is connected through a passage 95 in a chuck housing 56 to a chamber 58 into which the drill steel projects for receiving the blows of the striking bar. The passage tfli supplies pressure fluid from the valve chamber 39 to the forward end of the cylinder bore for moving the hammer piston through its rearward stroke. A passage liit'l opens at one into the exhaust port 53 and at its other end into the valve chamber 89 at the rearward end of the distributing valve 55. A slide valve I52 guided in a guideway Hi5 on the cylinder is provided with an operating handle Hi5, and when this valve is moved to the position shown in Fig. 6 the communication of exhaust port 93 and passage 95 with atmosphere is cut off. Arranged in the handle N25 is a plunger Hi5 pressed by a spring Ml into a detent recess N38 for holding the slide valve in its open position. With the slide valve in open position the distributing valve operates in its normal manner to control the supply of pressure fluid to the cylinder bore and effect reciprocation of the hammer piston. Any pressure fluid passing through the splineways Q to the chamber 98 is vented through passages 95 and 94 to atmosphere. When the slide valve i112 is moved to a position closing the exhaust port 93 and the discharge end of passage 94, pressure fluid flowing through the passage 99 to the forward end of the cylinder bore is prevented from escaping through the exhaust port 53 when it is overrun by the hammer piston. he pressure fluid then acts on the forward face of the piston to move it to the position shown in Fig. 6, and pressure fluid is supplied through the passage liiil to the rear end of the distributing valve for holding it in its position for supplying pressure fluid to the front end of the cylinder bore. A small vent port l iii opens through the walls of the cylinder into the rear end of the cylinder bore for conducting away any fluid compressed in the rear portion of the cylinder bore by the piston after it overruns the exhaust port 93 or leaking into the cylinder when the piston is in the position of Fig. 6. With an escape for presshut down.

sure fluidat the rear endof the cylinder bore the piston may be movedto its: extreme rearward positicn by the pressure fluid in the front end of the cylinder bore and assuremovement of the splineways 9 into the cylinder bore so that pressure fluid may passthrough them to the chamber 98 where it enters thebore 34 in the drill steel and is conducted-into the drill hole. Obviously, the closed condition of exhaust port 93 will limit the passage of air from the front end of the cylinder boreto flow through the spline- .ways to the chuck.

As a result of this invention, it will be noted that there is provided an improved hole cleansing means for a pneumatically operated rock drill. Itwill further be noted that by reason of the improved hole cleansing means there is obtained a venting of pressure fluid from the drill hole during operation of the drill and asupply of pressure fluid to the drill hole when the drill is The complete control of the drill and of the hole cleansing means is obtained, in some forms of the invention, through the manipulation of .a single manually operated valve. In each of the forms illustrated, manipulation of a single valve suflices to initiate hole blowing and to discontinue chuck venting or to stop hole blow- .ing and vent the chuck. .And means is provided in each of the illustrative species for minimizing the quantity of liquid required by reducing the tendency of air under pressure to enter the drill steel when normal drilling is in progress, while yet precluding the escape of air pressure when hole blowing is to be effected. Other uses and advantages of the improvedhole cleansing means will be clearly apparent to those skilled in the 1 art.

distribution means for effecting reciprocation of v said piston, a chuck for receiving and supporting the shank of ahollow drill steel, the chuck having a' chamber within which the rear end of the drill steel projects in a position to receive the impactblows of said piston, and'selectively operative ineans-for continuously supplying gaseous pressure-fluidto said chamber or for continuously connecting said chamber to atmosphere to preclude the building up of a pressure-therein and .thedelivery therefrom of gaseous fluid'pressure tothe hollow drill steel.

2. In a rock drill, a cylinder hav-ing'a'bore, a piston reciprocablein said bore, fluid distribution means for effecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shankv of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during the reciprocation of said piston, means for continuously venting pressure fluid from said chamber when said valve means is in a position for supplying presill sure fluid to said fluid distribution means, for discharging to atmosphere fluid which attains entry to said chamber from said cylinder bore, and means for cutting off said venting means and supplying pressure fluid to said chamber and to the drill hole through said hollow drill steel when said valve means is in a position for cutting oif fluidsupply tosaid distribution means.

3. In a rock drill, a cylinder having a bore, a piston reciprocable insaid bore and having a striking bar, fluid distributionmeans for effecting reciprocation of said piston, valve means for controllng the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows along said striking bar from said cylinder bore during the reciprocation of said piston, and pressure fluid venting and supply means for said chamber and including passage means opening into said chamber independently .of the cylinder bore and valve means for controlling communication of said passage means with atmosphere or with a source of pressure fluid supply.

4. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, fluid distribution means for eflecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinderbore during the reciprocation of said piston, means for continuously venting pressure fluid from said chamber when said valve means is in a position for supplying pressure fluid to said fluid distribution means, for discharging to atmosphere fluid which attains entry to said chamber from said cylinder bore, and means for cutting off said venting means and supplying pressure fluid to said chamber and to the drill hole through said hollow drill steel when said'valve means is in a position for cutting ofl fluid supply to saiddistribution means, said last mentioned valve means being movable with said first mentioned valve means and connecting said passage means with atmosphere when said first mentioned valve -means effects supply to said fluid distribution means.

5. In a rock drill, a cylinder having a bore, a' piston reciprocable in said bore, fluid distribution means for effecting reciprocation of said piston, valve means for controlling the supply of DIGSSlllf-J'flllld to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during the reciprocation of said piston, means for continuously venting pressure fluid from said chamber when said valve means is in a position for supplying pressure fluid to-said fluid distribution means, for discharging to atmosphere fluid which attains entry to said chamber from said cylinder bore, and means for cutting off said venting means and supplying pressure fluid to said chamber and to the drill hole through said hollow drill steel when .saidvalve -means is in a position for cutting off fluid supply to said distribution means, said last mentioned valve means being movable with said first mentioned valve means and connecting said passage means with atmosphere and pressure fluid supply when said first mentioned valve occupies positions, respectively, for eiiecting supply to and cutting off supply from said fluid distribution means.

6. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, fluid distribution means for effecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during reciprocation of said piston, means for conducting a cleansing liquid to the hollow drill steel including a liquid conducting tube extending axially through said cylinder and piston, valve means for controlling the flow of cleansing liquid through said liquid conducting tube, and pressure fluid venting and supply means for said chamber and including passage means opening into said chamber independently of the cylinder bore and valve means for controlling communication of said passage means with atmosphere or with a source of pressure fluid supply, said last mentioned valve means operative in one position thereof to vent to atmosphere pressure fluid which enters said chamber from said cylinder bore.

7. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, fluid distribution means for effecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during reciprocation of said piston, means for conducting a cleansing liquid to the hollow drill steel including a liquid conducting tube extending axially through said cylinder and piston, pressure fluid venting and supply means for said chamber including passage means opening into said chamber, and means for supplying cleansing liquid to said liquid conducting tube and for connecting said passage means continuously to atmosphere during the supply of pressure fluid to said fluid distribution means to discharge to atmosphere the fluid which enters said chamber from said cylinder bore.

8. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, fluid distribution means for eiiecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of th drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during reciprocation of said piston, means for conducting a cleansing liquid to the hollow drill steel including a liquid conducting tube extending axially through said cylinder and piston, pressure fluid venting and supply means for said chamber including passage means opening into said chamber, and

means for supplying cleansing liquid to said liquid conducting tube and for connecting said passage means to atmosphere independently of the cylinder bore during the supply of pressure fluid to said fluid distribution means to discharge to atmosphere the fluidwhich enters said chamber from said cylinder bore, said last mentioned means being operative to cut off the supply of cleansing liquid and thesupply of pressure fluid to said distribution means and to supply pressure fluid to said passage means. I

9. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, means for distributing pressure fluid to said cylinder bore and effecting reciprocation of said piston, an exhaust port for said cylinder bore, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore, means for venting said chamber continuously during the reciprocation of said piston to discharge from said chamber pressure fluid which enters it from said cylinder bore, and valve means for cutting 01f said exhaust port for said cylinder bore and said chamber venting means while pressure fluid continues to be supplied to said cylinder bore.

10. In a rock drill, a cylinder having a bore, a piston reciprocable in said bore, fluid distribution means for effecting reciprocation of said piston, valve means for controlling the supply of pressure fluid to said distribution means, a chuck for receiving and supporting the shank of a hollow drill steel, the chuck having a chamber within which the rear end of the drill steel shank projects in a position to receive the impact blows of said piston and into which pressure fluid flows from said cylinder bore during the reciprocation of said piston, and pressure fluid venting and supply means for said chamber and including passage means opening into said chamber independently of the cylinder bore and valve means for controlling communication of said passage means with atmosphere or with a source of pres sure fluid supply, said last mentioned valve means being continuously urged toward its position for connecting said passage means with atmosphere and operative on the supply of pressure fluid thereto for connecting said passage means with a source of pressure fluid supply.

11. In combination, a motor having a cylinder With a piston reciprocable therein, a hollow drill steel, means for supporting said drill steel in position for actuation by said piston, means for delivering a cleansing liquid to said hollow steel, means for delivering air under pressure to said hollow drill steel, said air and liquid delivering means having coordinated control means for interrupting air supply and venting the air delivering means continuously during liquid supply, and for interrrupting venting of the air delivering means and delivering air to the latter and concurrently interrupting liquid supply.

12. The combination defined in claim 11 in which the liquid and air delivering means each have an air pressure controlled control valve therein.

13. The combination defined in claim 11 in which the liquid and air delivering means each have an air pressure controlled control valve therein and in which a throttle valve for the motor is provided which governs also the supply of fluid to said air pressure controlled control valves: v

14. Incombination, a motor having a cylinder and-a piston-reciprocable insaid-cylinder, a hollow drill steel" having a rear end; positioned for actuation by said piston; a; throttle valve for said motor, means for conducting a-gaseous fluid from said-throttle valveto-said hollow steel or venting the-rear end of 'said steel to atmosphere, means for conducting a cleansing liquid to said drill 10- steel, saidthrottle valve including passages for controlling-the supply of operating'fluid to said motor and'also controlling the delivery of gaseous fluid and: liquid-to'the hollow steel, and means 

